1. Field of the Invention
The present invention relates to a thin film magnetic head.
2. Discussion of Background
Most thin film magnetic heads employed in magnetic disk devices constituting computer storage apparatuses at present are the combined type that are provided with a thin film write element and a magnetoresistive (MR) read element. MR read elements, which are not dependent upon the speed relative to the magnetic disk, are capable of achieving a high degree of resolution. An MR read element includes a first shield film, a second shield film and an MR element. The first shield film and the second shield film are provided over a distance from each other via an appropriate nonmagnetic insulator and the MR element is provided between the first shield film and the second shield film.
The write element, which is constituted of an inductive electromagnetic transducer, is laminated on the MR read element. An inductive thin film magnetic transducer to constitute the write element is provided with a first magnetic film which also functions as the second shield film for the MR read element, a second yoke, a gap film, a coil film supported by an insulating film and the like.
The front ends of the first magnetic film and the second yoke are respectively constituted of a first pole tip and a second pole tip that face opposite each other over the gap film having a very small thickness, and a write operation is performed at the first and second pole tips. The first magnetic film and a second magnetic film are linked with each other so that their yokes complete a magnetic circuit at a back gap portion located on the opposite side from the first and second pole tips. The coil film is formed winding around the linking area of the yokes in a coil.
In order to support high recording density using this type of thin film magnetic head, the quantity of data stored per unit area of the magnetic disk (areal density) must be increased. An improvement in the areal density is achieved by improving the performance of the magnetic recording medium such as a magnetic disk and increasing the frequency at the write circuit as well as by improving the capability of the write element.
In one of the means for increasing the areal density by improving the capability of the write element, the gap length between the pole tips is reduced. However, since a reduction of the gap length leads to a reduction in the recording magnetic field intensity between the pole tips, there is naturally a limit to the degree to which the gap length can be reduced.
In another means for increasing the areal density, the number of data tracks that can be recorded on the magnetic disk is increased. The number of tracks that can be recorded on a magnetic disk is normally expressed as TPI (tracks per inch). The TPI capability of a write element may be enhanced by reducing the size of the head that determines the width of the data tracks. The head size is normally referred to as the head track width.
In the case of a conventional thin film magnetic head in the prior art described above, since the first magnetic film at the write element is also employed as the second shield film of the MR read element, the width of the lower portion cannot be reduced, and consequently, a rather large side fringing magnetic field is generated during a recording operation. This magnetic field is caused by a leak of magnetic flux from the second pole tip whose width is reduced to the first magnetic film whose width is not reduced. Such a side fringing magnetic field restricts the lower limit of width that can be achieved and limits the degree to which the track density can be improved. In addition, it degrades the off-track performance when track data that have been written are read by the MR element.
As a means for eliminating the problem discussed above, Japanese Unexamined Patent Publication No. 262519/1995 and Japanese Unexamined Patent Publication No. 225917/1995 disclose a means for adjusting the width of the lower portion to the width of the second pole tip through ion beam milling.
In addition, U.S. Pat. No. 5,600,519 discloses a structure provided with a tapered portion between the zero throat point and an expanded portion at the first magnetic film and the second magnetic film.
Furthermore, U.S. Pat. No. 5,452,164 discloses a structure achieved by setting the width of the second yoke larger than the width of the second pole tip so that the two side surfaces of the second yoke in the widthwise direction project out from the two side surfaces of the second pole tip.
However, when the track width at the head is reduced, magnetic saturation tends to occur at the pole tips, which results in degradation of the recording magnetic field pitch and causes the magnetic field to readily leak through the two sides of the pole tip in the direction of its width to induce recording bleed due to the leaked magnetic field. None of the publications on the prior art technologies disclose a means for solving this problem.
It is an object of the present invention to provide a separate type thin film magnetic head in which the yokes and the pole tips are separated.
It is a further object of the present invention to provide a separate type thin film magnetic head with which magnetic saturation at the pole tips can be prevented to eliminate problems of degradation in the recording magnetic field pitch and recording bleed occurring due to leaked magnetic field.
In order to achieve the objects described above, the thin film magnetic head according to the present invention is provided with at least one write element. In the write element, which includes a first pole portion, a second pole portion and a gap film, the gap film is provided between the first pole portion and the second pole portion. The second pole portion includes a third magnetic film and a fourth magnetic film, with the third magnetic film provided adjacent to the gap film and the fourth magnetic film provided adjacent to the third magnetic film. The third magnetic film has a width W20 at a position receding from its surface facing opposite the medium, which is larger than its width W21 at the surface facing opposite the medium.
As described above, in the thin film magnetic head according to the present invention, the third magnetic film of the second pole portion is adjacent to the gap film. Consequently, by using the third magnetic film as a pole tip and setting the head size that determines the width of the data tracks to very small dimensions determined by the width of the third magnetic film to improve the TPI capability, high density recording is achieved.
At the same time, the fourth magnetic film included in the second pole portion is provided adjacent to the third magnetic film. By using the fourth magnetic film as a yoke, the magnetic flux which is required for a write operation can be supplied to the third magnetic film constituting the pole tip from the fourth magnetic film. In other words, according to the present invention, a separate type thin film magnetic head in which the pole tip is separated from the yoke can be achieved.
According to the present invention, the third magnetic film has the width W20 at a position receding from its surface facing opposite the medium, which is larger than the width W21 at the surface facing opposite the medium. This structure prevents magnetic saturation from occurring at the pole tip constituted of the third magnetic film to eliminate the problems of degradation of the recording magnetic field pitch and recording bleed occurring due to a leaked magnetic field.
In one specific mode of the thin film magnetic head according to the present invention, the first pole portion includes a first magnetic film and a second magnetic film. The second magnetic film is provided adjacent to the gap film, whereas the first magnetic film is provided adjacent to the second magnetic film. By combining this structure for the first pole portion and the structure of the second pole portion described earlier, a structure which is achieved by providing the first magnetic film, the second magnetic film, the gap film, the third magnetic film and the fourth magnetic film adjacent to each other in this order is realized. By adopting this structure, in which the second magnetic film and the third magnetic film among the four magnetic films, i.e., the first magnetic film to the fourth magnetic film, are employed as pole tips, the head size which determines the width of the data tracks can be set very small, determined by the widths of the second magnetic film and the third magnetic film to increase the TPI capability so that high density recording can be achieved.
In addition, the first magnetic film and the fourth magnetic film may be extended toward the rear from the pole portions to constitute yokes with the portions extended toward the rear. In this structure, the magnetic flux required for a write operation is supplied from the first magnetic film and the fourth magnetic film constituting the yokes to the second magnetic film and the third magnetic film constituting the pole tips.
The present invention further discloses pole dimensions that are effective for maintaining the write magnetic field and preventing recording bleed from occurring due to a leaked magnetic field.
The thin film magnetic head according to the present invention normally includes an MR read element. In the MR read element, which includes a first shield film, a second shield film and an MR element, the first shield film and the second shield film are provided over a distance from each other with the MR element located between the first shield film and the second shield film.
The write element is laminated on the MR read element. In this structure, the second shield film also functions as the first magnetic film of the write element to achieve a reduction in thickness.